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West Nile Virus Encephalitis

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									  West Nile Virus

          Paul R. Earl
   Facultad de Ciencias Biológicas
Universidad Autónoma de Nuevo León
    San Nicolás, NL 66451, Mexico
In North America since 1999, West Nile Virus
(WNV) has joined the other major viruses like
dengue that cause various encephalites. WNV
as new is clinically little known and its role in
public health (PH), epidemiology, surveilance
and vector (mosquito) control is still illdefined.
WNV is one more PH cost. Costs range from
hospital bed time and clinical labor, loss of
work hours and school time to other costs like
reagents for immunological diagnosis. Birds
(especially crows), horses and man are the
most noteworthy in a very wide range of WNV
hosts. During 1999-2002, WNV was detected
in 36 mosquito species in the US.
WNV is a member of the family Flaviviridae
which seems very close to Togaviridae.
Serologically, it is a member of the Japanese
encephalitis virus antigenic complex, which
includes St. Louis, Japanese, Kunjin and
Murray Valley encephalitis viruses. WNV was
first isolated in Uganda in 1937.

The 2002 WNV epidemic and epizootic resulted
in reports of 4,156 reported human cases of
this disease (including 2,942
meningoencephalitis cases and 284 deaths),
16,741 dead birds, 6,604 infected mosquito
pools and 14,571 equine cases.
The central problem is morbidity
and mortality by encephalites in
man, domestic and wild animals
 caused by different mosquito-
 borne viruses throughout the
It is much more important to deal with the
entire group of encephalitis viruses and
dengue than it is to dwell on WNV. There
SHOULD BE much better PH orientation to
the geographies and seasonalities of all these
viruses from local to continental levels.
Medical and veterinary forces need better
mutual understanding and interaction.
Climate, vector control and surveillance are
often neglected topics. Cyclonic winds have
strong yet little known epidemiologic effects.
What is the risk of infection? Of what or
whom? By what !! ?
What are the public sentiments ?
Somehow, there is a feeling of
professional NEGLECT. Neglect relates
to ignorance. Much of the public has
been hardened by its previous disease
experiences. In its turn, this relates to
POLITICAL WILL. In the end or in many
situations, the public must DEMAND
PROTECTION in order to get it. Of
course, the public best understand the
RISK so that it will pay the taxes
needed to reduce the risk. Where do
your tax dollars go ? If you replied,
“Into vector control,” that would be a
reasonably good joke.
   So we have more than WNV. We have a
group of viruses with much in common that
are clinically little known. Let us say that the
index of suspicion is close to zero.
   What is it that we need to know ? The risk.
Then pay taxes in PH terms to reduce the risk.
This is the old erratic and encephalitic risk that
WNV is increasing.
   People will pay willingly for mosquito control
if they understand the risks to their health.
The community MUST REALIZE that it MUST
DUMP all standing water ! Public education
for awareness of arboviruses and other agents
is desired at the primary school level.
Encephalites of various causes
and knowing the risk
What are these virusus?
They are: 1/ WNV, 2/ dengue (DEN),
3/ Venezuelan Equine Encephalitis Virus
(VEEV), 4/ St Louis Encephalitis Virus (SLEV),
5/ Western Equine Encephalitis (WEEV) and
6/ Eastern Equine Encephalitis (EEEV). Yellow
Fever and Powassan encephalitis/ meningitis
and the California serogroup viral
encephalitis/meningitis, including infections
with the following viruses: La Crosse,
Jamestown Canyon, Snowshoe Hare,
Trivittatus, Keystone and the California
encephalitis viruses
We have come a long way—perhaps—from
WNV, because it is part of an international
problem, not the problem itself. The problem
involves the costs and methods of MOSQUITO
CONTROL. It ACUTELY involves the public
recognition of disease transmission. Many
citizens do know that these diseases are
insect-transmitted, but what percent of
people, where, etc. is of course not known.
They do not know the symptoms, meaning
that they do not recognize the disease.
Questionaires don‟t seem to be used.
Do we want to know WHEN the risk
becomes intolerable and how to control it?
     International surveillance
On the surface it seems like a good idea to
coordinate insect surveillance among Canada,
USA & Mexico, partly because territories from
the equator to northern Canada are involved.
However, it‟s a long way from good, because
financing at all levels will raise conflicts. Is the
risk great enough to demand international
surveillance? Probably not. Many inland disease
outbreaks are local ones. Mexico is almost
singular, because it absorbs shocks from both
the Eastern Pacific & Atlantic Hurricane Centers.
Some of these 2 winds running over 100 km/hr
mix in the Gulf of Mexico and go straight north
into Texas and Louisiana.
         Research objectives
As given by CDC, these include: a) Current and
Future Geographic Distribution of WNV, b) Bird
Migration as a Mechanism of WNV Dispersal,
c) Vector and Vertebrate Host Relationships
and Range, d) Virus Persistence Mechanisms,
e) Mosquito Biology, Behavior, Vector
Competence, Surveillance, and Control,
f) Development and Evaluation of Prevention
Strategies, g) Laboratory Diagnosis, h) Clinical
Spectrum of Disease and Longterm Prognosis in
Humans, i) Risk Factor Studies, j) Detailed Clinical
Descriptions and Outcome in Human Cases, k)
Viral Pathogenesis, l) Genetic Relationships and
Molecular Basis of Virulence,
           WNV facts

WNV has been found in humans,
horses, birds and other animals,
typically in Africa, Eastern Europe
and the Middle East. In 1999, WNV
was detected in the US (NY, NJ) for
the first time, and since then it has
spread across North America,
including Mexico.
WNV exists in nature through a
transmission cycle involving mosquitoes,
birds and horses. Mosquitoes become
infected with WNV when they feed on
infected birds, which may carry the virus
in their blood for a few days. Infected
mosquitoes can then transmit this new
virus to humans and animals. when biting
to take a blood meal. In rarest instances,
WNW may be transmitted from human to
human through organ donation or blood
transfusion or from pregnant mother to
Most individuals infected with WNV will not
have any symptoms or signs of illness. People
who do develop illness may experience mild
symptoms such as fever, headache and body
aches. Occasionally a skin rash and swollen
lymph glands may occur. These symptoms
generally appear 3-14 days following the bite
of an infected mosquito. Less than 1% of
persons infected with the virus will develop
more severe disease with symptoms such as
high fever, neck stiffness, stupor,
disorientation, coma, tremors, convulsions,
muscle weakness, paralysis and, most rarely,
a) Total leukocyte counts in peripheral blood
were mostly normal or elevated, with
lymphocytopenia and anemia also occurring,
b) Hyponatremia was sometimes present,
particularly among patients with encephalitis,
c) Examination of the cerebrospinal fluid (CSF)
showed pleocytosis, usually with a
predominance of lymphocytes, d) Protein was
universally elevated, e) Glucose was normal,
f) Computed tomographic scans of the brain
mostly did not show evidence of acute disease,
but in about 1/3 of patients,
g) magnetic resonance imaging showed
enhancement of the leptomeninges, the
periventricular areas or both.
Reducing risk is avoiding mosquitoes.
1/ Dump all standing water to inhibit
mosquitoes from breeding, 2/ Stay indoors at
dawn or early in the evening, 3/ Wear long-
sleeved shirts and long pants when going
outdoors, 4/ Spray clothing with repellents
containing permethrin or DEET (N, N-diethyl-
meta-toluamide), 5/ Apply insect repellent
sparingly to exposed skin and following all
packageinstructions. 6/ Ensure that all
window screens in your home or business are
intact and do notcontain holes. Repair any
damaged screens.
The Fort Dodge Animal Health West Nile
Virus Vaccine approved by the US
Department of Agriculture (USDA) is
safe. Millions of vaccine doses have been
used since the USDA approved its use in
2001. The Center for Veterinary Biologics
within USDA's Animal and Plant Health
Inspection Service maintains a tollfree
telephone hotline (800-752-6255) and a
mailbox on its Web site
( and
encourages veterinarians and other
vaccine consumers to report problems
with vaccines.
Does the WNV vaccine also have DEN1-4 and
Of course not. Does it include SLEV and EEEV?
Of course not. What proteins of the envelope
genes of these similar viruses are used now in
vaccines? What is a plasmid ?
The objective would be to produce a
protective vaccine against 1/ WNV, 2/ VEEV,
3/ EEEV, 4/SLEV and the 4 serotypes of
dengue (DEN1-4). This is technically possible
with plasmids and can solve many very
expensive epidemiologic problems. Such
outbreaks are EXPENSIVE to owners by
animal loss.
One aspect of biotechnology—or industry—is
that a pharmaceutical company will not do
research or produce a vaccine in order to lose
money. WNV vaccine is produced in the US.
VEE vaccine is not produced in Mexico. This
reflects the horse owners willingness and
ability to pay.
We want this multivaccination to go through
one month before victims of a future epidemic
begin to show, but—incredibly—will accept a
week‟s time. The organizational effort needed
to stop an ongoing viral epidemic—with
properly identified viruses—is likely too slow.
           Mosquito control
Standard mosquito control measures for city
populations such as one plagued by dengue
may have to be vastly expanded in the
countryside if the aim is to restrict an
epidemic. Note that as epidemic applies to
people, epizootic applies to animals, but that
„epidemic‟ is often also used for animals. Still,
the point here is that huge rural areas are not
like civic ones, especially when mountains are
involved. Regardless, fast streams with banks
unimpeded by brush may not be too difficult
to control chemically over rather great
distances in the hundreds of km.
Advantages of mosquito-based surveillance
include the following:
1/ The virus invader can be identified.
2/ It may provide the earliest evidence of
transmission in an area. 3/ It helps establish
information on potential mosquito vector
species. 4/ It provides an estimate of vector
species abundance. 5/ It gives quantifiable
information on virus infection rates in different
mosquito species. 6/ It provides quantifiable
information on potential risk to humans and
animals. 7/ It provides baseline data that can
be used to guide emergency control operations.
8/ It allows evaluation of control methods.
  Surveillance is a warning system
that can often save both human and
animal lives. An ounce of prevention
      is worth a pound of cure !

Surveillance is UNPOPULAR via its costs. What
are the costs with and without surveillance
with or without chemical control? They are
UNKNOWN and most difficult to estimate. We
ASSUME that vigilance pays without even an
approach to controling some future epidemic
that cannot be defined. This is a typical
undefined problem of preventive medicine. If
the problem were profitably solved, of course,
the solution would be APPLIED, but this is not
the case. Finally, one is reminded of the huge
populations in millions that cover these vast
territories. Obviously, the magnitude of the
viral encephelitis problem might result in an
equivalent surveillance cost.
      New and little known

Although the invasion of New York City by
WNV in 1999 was a new epidemic therefore
not then known, encephalitis-causing viruses
are wellknown and most are worldwide. The
PH steps to be taken remain irresolute, and
what is taught in the classroom is unsettled.
What relevent information is the 10th grader
getting? The public appreciates WNV as a
new threat via TV, but not its inner workings.
What is still lacking is the empirical
experience in epidemics, and the detailed
data of epidemic progress.
The control of a virus outbreak is far from
simple, often having local unknowns. The
encephalitis virus result is often: 1/ dead or
2/ immune. At this conjuncture, the epidemic
is over. For Part 2, either natural or arificial
immunization serves. Of course, the difficulty
is correctly attributing the cessation of the
epidemic. Having too few mosquitoes (Choice
3) can—most obviously—stop the outbreak,
leaving susceptibles. Choice 3 might be a
larvicide campaign, reducing the number of
mosquitoes. Again, we have cost and risk. It
may take some deep thinking to work these
things out.

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